An organic EL display is self-emissive and thus adapted to high contrast and quick response, and therefore appropriately used in a motion picture application, such as for a television and so forth, which shows a natural image. The organic EL element attains multi-level tones, or gradation, by driving using a constant current via a control element such as a transistor or the like or by driving using a constant voltage and changing the light emission period.
In driving using a constant current, the transistor operates in a saturation region, consuming a larger amount of power. Therefore, driving using a constant current is preferably not used, in order to reduce power consumption. In digital driving using a constant voltage, on the other hand, a transistor operates in a linear region, which can reduce an amount of power consumed by the transistor. (See WO 2005/116971)
In digital driving using a constant voltage, however, the same pixel needs to be accessed a multiple number of times during one frame period when a sub-frame is used, as each pixel has only a one-bit gradation capacity. This requires a high speed operation, thus making it difficult to attain gradation in high-resolution display. Also, in digital driving using a plurality of sub-frames having different light emission intensities, bit data needs to be written into a plurality of corresponding sub-pixels at a high speed. This makes it difficult to attain high resolution display.
In either manner of digital driving, the frequency at which to access a pixel increases with high resolution and gradation display, which increases the power consumption by the driving circuit. In particular, an increase of the display size results in an increase of power consumption by the driving circuit, and an increase of the frequency due to higher resolution display results in difficulty in reducing power consumption.